Device for controlling an electric motor

ABSTRACT

The present invention concerns a device ( 20 ) for controlling an electric motor ( 1 ) including a rotor ( 6 ) and at least three stator coils ( 2, 3, 4 ) connected between three connection terminals, means ( 5 ) for providing three control signals (Ua, Ub, Uc) to said connection terminals, and means ( 22 ) for dectecting said rotor angular postion. Said dectecting means include measuring means ( 24 ) designed to be connected to the motor, such that the means form with said coils at least two oscillating circuits supplying two respective signals (U 1,  U 2 ) at two measurement frequencies respectively which are themselves periodic functions of said rotor angular position, and means ( 26 ) for calculating a single value corresponding to the two measurement frequencies, this value being the desired angular position.

BACKGROUND OF THE INVENTION

The present invention concerns the field of electric motors including atleast three stator coils and, more particularly, a device forcontrolling such a motor including detecting means for detecting theinstantaneous angular position of a rotor.

A <<brushless motor>> or a motor with no commutator>> is defined in thepresent description as a direct current electric motor which includes amobile part (or <<rotor>>) provided with a permanent magnet, and a fixedpart (or <<stator>>) provided with at least three fixed bipolar coils.In the event that the motor includes three stator coils, they arearranged so as to be staggered at 120° to each other. A motor of thistype has the advantage of being able to be sterilized, for example in anautoclave, unlike motors with brushes, whose brushes decompose duringsterilization. The question of sterilization thus becomes a primaryconcern, in particular in application fields requiring optimum sanitaryhygiene, such as the field of medical instruments.

FIG. 1 shows schematically a brushless motor 1 provided with threestator coils 2 to 4, the motor being controlled by a conventionalvoltage generator 5. For this purpose, each of coils 2 to 4 includes aconnection terminal. References 2 a, 3 a and 4 a respectively designatethe connection terminals of coils 2, 3 and 4. Generator 5, includesthree connection terminals 5 a, 5 b and 5 c connected respectively toterminals 2 a, 3 a and 4 a, and it is arranged to be able to provide,via terminals 5 a to 5 c, three respective electric voltages Ua to Uc tothe three respective coils 2 to 4, which achieves the control of motor1.

FIG. 2 shows three timing diagrams 10 to 12 of voltages Ua to Uc whenthe motor of FIG. 1 is being controlled. It will be noted that the setof these three voltages constitutes a three phase system formed ofsquare periodic signals, these signals having the same amplitudedesignated A and the same period designated T, and being phase shiftedby T/3 with respect to each other. In FIG. 2, the reference t0designates any initial instant.

When voltages Ua to Uc of FIG. 2 are applied to the respective coils 2to 4 of FIG. 1, the coils can be polarized sequentially in accordancewith six different states. The first state corresponds to the intervalof time comprised between instant t0 and t0+T/6, during which voltagesUa, Ub and Uc respectively have the value A, 0 and A. The second statecorresponds to the interval of time comprised between instants t0+T/6and t0+2T/6, and so on. As a result of this polarization, a rotatingfield able to cause the rotor to rotate is generated, the permanentmagnet of the rotor being arranged in close proximity to coils 2 to 4.By way of example, the rotational speed of the rotor can vary between 0and 40,000 tr/min, and the frequency F0 corresponding to period T can becomprised between 1 and 667 Hz.

One problem encountered with a control of this type is that it isnecessary to detect the instantaneous angular position of the rotor. Inorder to cause the rotor to rotate to a desired angular position, therotor angular position must be detected at the instant when controlvoltages are applied to the stator coils, so that the values of thevoltages applied can create, in the air gap, a magnetic field able tocause the rotor to rotate from the angular position thus detected to thedesired angular position.

A first conventional solution to the problem of detecting the rotorangular position consists in fitting such a motor with a coding devicewhich is linked to the rotor, and which controls the switching of theelectric voltages applied to the stator coils. For example, contactlesselectronic sensors are commonly used to detect the rotor angularposition, said coding device including a magnet which rotates with therotor, and several cells or Hall effect sensors situated in the field ofthe magnet, and fixed to the stator so as to switch when there aremagnetic field reversals. It will be recalled that a Hall effect cell isarranged to be able to detect the variations in a neighbouring magneticfield.

A solution of this type has various drawbacks. In particular, Halleffect cells are relatively expensive and the mounting thereof inproximity to the motor increases the space requirement of the latter.Furthermore, it is necessary to use, in addition to the three powersupply wires of the motor, two wires for supplying power to the Halleffect cells and three wires for collecting the data provided bythereby. It goes without saying that the arrangement of an instrumentwith eight wires goes against constraints as to handling ability,sterilization, weight, robustness and cost, these constraints beingcommon in industry, in particular within the field of medicalinstruments.

A second conventional solution to the problem of detecting the rotorangular position consists in measuring the back-electromotive forcewhich is proportional to the rotational speed of the rotor and which,consequently, can provide data relating to its movement and thus to thespeed of the rotor.

One drawback of such a solution lies in the fact that it does not allowthe rotor angular position to be detected directly.

Another drawback of this solution lies in the fact that this forcedecreases with the rotational speed of the rotor, which makes itdifficult to measure.

Another drawback of this solution lies in the fact that detection of theinstantaneous position of the rotor disturbs the normal operation of themotor. The back-electromotive force measurement can not be performedsimultaneously with the supply of the motor control voltages. Thus, theworking of the motor is interrupted at each back-electromotive forcemeasurement.

It has thus been observed that all the solutions proposed in the stateof the art to answer the aforementioned problem were not satisfactoryfor, on the one hand, detecting the instantaneous angular position ofthe rotor and, on the other hand, answering constraints or concernsbelonging to specific application fields, for example for controlling abrushless motor in a dental instrument. Also by way of example, withinthe scope of an application to robotics, the conventional solutions donot allow the rotation of the rotor from a predetermined angle to becontrolled with sufficient precision and with a small number of leadwires.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a control device ableto be connected to a brushless motor, this device overcoming theaforementioned drawbacks and, in particular, being able to detect theinstantaneous angular position of the motor rotor.

Another object of the present invention is to provide a control deviceable to be connected with a minimum of connecting wires, so as to answerthe constraints as to handling ability, weight and cost, suchconstraints being common in industry, and in particular in the field ofmedical instruments.

Another object of the present invention is to provide a control deviceable to detect the instantaneous angular position of the rotorindependently of the rotational speed of the rotor, even if the rotorhas stopped.

Another object of the present invention is to provide a control deviceable to detect the instantaneous angular position of the rotor withoutdisturbing the normal operation of the motor.

Another object of the present invention is to provide a control deviceanswering the constraints as to sterilization and robustness, inparticular for an application in the field of medical instruments.

These objects, in addition to others, are achieved by the control deviceaccording to claim 1.

The device according to the invention includes detecting means whichhave the advantage of providing at least two measurement signals atrespective frequencies which together represent the rotor angularposition, and that the supply of these signals is independent of thenormal operation of the motor, in particular the control of the latterby the power supply means.

Another advantage of these detecting means lies in the fact that theyare connected to the power supply wires connecting the motor to thepower supply means, without requiring additional connections between themotor and the detecting means to be able to detect the rotor angularposition. As a result, the motor fitted with such an acquisition deviceanswers the concerns as to handling ability, robustness and weight,which are common in industry, in particular in the field of dentalinstruments.

The device according to the present invention further includes filteringmeans which have the advantage of filtering the measurement signalsacross the output terminals of the power supply means, so as to assurethat the supply of these signals does not disturb the control of themotor by the power supply means.

The device according to the present invention further includesmeasurement means which have the advantage of providing the measurementsignals whose frequencies are higher than the frequency of the controlsignals, and whose amplitudes are lower than said control signals, sothat the measurement signals do not interfere with the control signalswhen the motor is controlled, so as to assure that the supply of thecontrol signals does not disturb the control of the motor via the powersupply means.

Another advantage of the detecting means lies in the fact that theyinclude inexpensive, non complex and compact electronic components,which answers the usual industrial concerns as to price, rationalizationand compactness.

Another advantage of the control device according to the presentinvention lies in the fact that they allow, in particular when the rotorhas stopped, the instantaneous angular position of the rotor to bedetected, without inducing any effect on the inductive distribution ofthe rotating field present in the motor air gap. Those skilled in theart will note that the measurement signals at their respectivefrequencies can be provided for any value of the rotational speed of therotor, and in particular when the rotor has stopped, since the detectionof the angular position is derived from the measurement of themeasurement frequencies which are provided independently of the controlof the motor by the power supply means.

Another advantage of the control device according to the presentinvention lies in the fact that it allows the instantaneous angularposition of the rotor to be detected with a precision of the order of adegree, which answers a demand for precision, which is common inindustry, in particular in the field of robotics and dentalimplantology.

The device according to the present invention further includesprocessing means which have the advantage of comparing the calculatedangular position with a comparison value, which allows the evolution ofthe angular position to be monitored over time.

Another advantage of these processing means lies in the fact that theyallow the number of revolutions made by the rotor to be calculated, waswell as the rotor speed and acceleration, which allows the evolution ofthese parameters to be monitored over time.

BRIEF DESCRIPTION OF THE DRAWINGS

These objects, features and advantages of the present invention, inaddition to others, will appear more clearly upon reading the detaileddescription of two preferred embodiments of the present invention, givensolely by way of example, in relation to the annexed drawings, in which:

FIG. 1, which has already been cited, shows schematically a conventionalbrushless motor controlled by a conventional voltage generator;

FIG. 2, which has already been cited shows three timing diagrams ofcontrol voltages of the motor of FIG. 1;

FIG. 3 shows a block diagram of a control device according to thepresent invention connected to the motor of FIG. 1;

FIG. 4 shows a first embodiment of the device of FIG. 3;

FIGS. 5 and 6 shows two electric configurations of the device of FIG. 4;

FIG. 7 shows two curves illustrating the temporal evolution of ameasurement signal associated with the configuration of FIG. 5, when therotor is in two respective angular positions;

FIG. 8 shows two curves illustrating the relations between the rotorangular position and two measured frequencies associated with theconfigurations of FIGS. 5 and 6;

FIG. 9 shows in more detail calculating means associated with the deviceof FIG. 4;

FIG. 10 shows a timing diagram of a signal provided by the calculatingmeans of FIG. 9, to control the configurations of FIGS. 5 and 6; and

FIG. 11 shows a second embodiment of the device of FIG. 3.

FIG. 3 shows a block diagram of a control device according to thepresent invention designated by the reference 20. This device isarranged and connected to a motor similar to motor 1 of FIG. 1, so as tocontrol the latter. It will be noted in FIG. 1 that elements of controldevice 20 which are identical to those described in relation to FIG. 1,have been designated by the same references.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 5 shows a block diagram of a control device according to thepresent invention designated by the reference 20. This device isarranged and connected to a motor similar to motor 1 of FIG. 1, so as tocontrol the latter. It will be noted in FIG. 1 that elements of controldevice 20 which are identical to those described in relation to FIG. 1,have been designated by the same references.

Motor 1 is connected to power supply means forming supply means similarto generator 5 of FIG. 1. It will be recalled that voltage generator 5is arranged to connect coils 2 to 4 successively to a power source whichis not shown, so as to provide voltages Ua, Ub and Uc to coils 2 to 4 asis shown in timing diagrams of FIG. 2. The connections of voltagegenerator 5 are achieved in response to a signal U0 which is compatiblewith the proper operation of voltage generator 5, the supply of thissignal being described hereinafter.

Control device 20 includes means 22 for detecting the angular position θof the rotor. Detecting means 22 include means 24 for measuring twodistinct different frequencies F1 and F2, measuring means 24 supplyingtwo signals U1 and U2 at two respective frequencies F1 and F2. Detectingmeans 22 further include means 26 for calculating angular position θfrom the two signals U1 and U2, and for providing this position in theform of signal U0.

FIG. 4 shows a first embodiment of device 20, in particular of measuringmeans 24.

Measuring means 24 include a switching circuit 34 including a firstgroup of terminals 34 a to 34 c, a second group of terminals 34 d to 34f and a control terminal 34 g. Switching circuit 34 is arranged to beable to receive a control signal U3 via terminal 34 g, and in responseto connect terminals 34 a to 34 c on the one hand, to terminals 34 d to34 f on the other hand, in accordance with two electric configurationsY1 and Y2 described hereinafter in relation to FIGS. 5 and 6. It will benoted that the supply of signal U3 is described in more detailhereinafter in relation to FIG. 10. Switching circuit 34 is preferablymade using switches formed by known electronic components, which performthe connections of configurations Y1 and Y2.

Measuring means 24 further include an amplification circuit 35 intendedto provide periodic signals U1 and U2 respectively at frequencies F1 andF2, when switching means 34 are in the respective configurations Y1 andY2. In the example of FIG. 4, amplification circuit 35 includes anoperational amplifier 36 whose output is connected, via a capacitor 37,to terminal 34 d. The non-inverting input (or <<+>> terminal) ofoperational amplifier 36 is connected, on the one hand, to terminal 34 evia a capacitor 38, and on the other hand to the device's earth via aresistor 39. The inverting input (or <<−>> terminal) of operationalamplifier 36 is connected, on the one hand, to terminal 34 f via acapacitor 40, and on the other hand to the device's earth via a resistor41.

The two configurations Y1 and Y2 of switching circuit 34 will now bedescribed. FIGS. 5 and 6 show the electric diagrams of measuring means24 of FIG. 4, in accordance with the respective configurations Y1 andY2. In the following description, the references Y1 and Y2 will alsodesignate the electric diagrams of measuring means 24 connected to motor1 via switching circuit 34, in accordance with the two respectiveconfigurations thereof Y1 and Y2. It will be noted in FIGS. 5 and 6 thatthe elements of control device 20 which are identical to those describedin relation to FIG. 4 have been designated by the same references.

In configuration Y1, as shown in FIG. 5, switching circuit 34 isarranged so that terminals 34 a to 34 c are respectively connected toterminals 34 d to 34 f. In other words, in configuration Y1, the outputof operational amplifier 36 is connected to terminal 2 a of motor 1, viacapacitor 37, and the non-inverting and inverting inputs of theamplifier are connected respectively to terminals 3 a and 4 a. Thus, inconfiguration Y1, measuring means 24 (i.e. switching circuit 34 andamplification circuit 35) and coils 2 to 4 form a first oscillatingcircuit in which the output of operational amplifier 36 supplies, viacapacitor 37, signal U1 to coil 2 and to calculating means 26.

Those skilled in the art will note that signal U1 is periodic atfrequency F1 which depends in particular on the impedance seen from the<<+>> and <<−>> terminals of operational amplifier 36. This impedancedepends directly on the inductance of coils 2 to 4. Moreover, it isknown that the inductance of a winding or a coil depends not only on itsstructure, but also on the intensity of the magnetic field which passesthrough it. Thus, in the case of motor 1, coils 2 to 4 are magneticallycoupled to the permanent magnet of the rotor, and part of the magneticfield generated by the magnet, which depends on angular position θ ofthe magnet with respect to the coil concerned, passes through each ofcoils 2 to 4. In other words, frequency F1 depends on angular position θof the rotor.

Purely by way of illustration, FIG. 7 shows two curves 50 and 51illustrating the temporal evolution of signal U1, when the rotor isrespectively in a first angular position θ0 or reference position and ina second angular position θ1 different to the reference position. Curves50 and 51 of FIG. 7 were measured experimentally, for the purpose ofdemonstrating the sensitivity of frequency F1 as a function of angularposition θ. Thus, frequency F1 (θ0) was measured as equal to 1.43 MHz,and frequency F1 (θ1) as equal to 1.3 MHz, i.e. a frequency differenceequal to 130 MHz between angular positions θ0 and θ1.

Those skilled in the art will also note that frequency F1 variesperiodically with angular position θ, at a period which corresponds to arotor rotation of 360° divided by the number of poles of the magnet ofthe rotor. In the present case, since this number is equal to 2, theperiod of variation in frequency F1 therefore corresponds to a rotationof 180° of the rotor.

Purely by way of illustration, FIG. 8 shows a curve 61 illustrating thevariations in frequency F1 as a function of angular position θ. Thereferences Fmin and Fmax designate respectively the minimum and maximumvalues of frequency F1.

In configuration Y2, as shown in FIG. 6, switching circuit 34 isarranged so that terminals 34 a to 34 c are connected respectively toterminals 34 e, 34 d and 34 f, which forms said configuration Y2. Inother words, the output of operational amplifier 36 is connected toterminal 3 a of motor 1, via capacitor 37, and the non-inverting andinverting inputs of the amplifier are connected respectively toterminals 2 a and 4 a. Thus, in configuration Y2, measuring means 24(i.e. switching circuit 34 and amplification circuit 35) and coils 2 to4 form a second oscillating circuit in which the output of operationalamplifier 36 provides, via capacitor 37, signal U2 to coil 3 and tocalculating means 26.

FIG. 8 also shows a curve 62 illustrating the variations in frequency F2as a function of angular position θ. As this Figure shows, likefrequency F1, frequency F2 varies periodically between a minimum valueand a maximum value, with a period which corresponds to a rotation of180° of the rotor. It goes without saying that the minimum and maximumvalues of frequency F2 are equal respectively to those of frequency F1,to the extent that coils 2 to 4 are symmetrical, and have the samenumber of turns and the same inductance. Moreover, it will be noted inFIG. 8 that curve 61 associated with frequency F1 is phase shifted by120° with respect to curve 62 associated with frequency F2. Thoseskilled in the art will easily understand that this phase shift derivesfrom the arrangement of coils 2 to 4 in motor 1, and the bipolar magnet,in this example, of the rotor.

Those skilled in the art will note that the supply of signals U1 and U2at respective frequencies F1 and F2 must not disturb the normaloperation of motor 1, i.e. the control of motor 1 by voltage generator5.

For this purpose, amplification circuit 35 is arranged so that theamplitudes of signals U1 and U2 are substantially lower than those ofvoltages Ua to Uc, and that the minimum values of frequencies F1 and F2are substantially higher than the maximum value of frequency F0 ofvoltages Ua to Uc. Moreover amplification circuit is arranged so thatthe maximum value of frequencies F1 and F2 are substantially lower thanthe value of the frequency of the signal used during electromagneticcompatibility tests which are commonly practiced in particular in thefield of dental instruments, the minimum frequency used duringelectromagnetic compatibility tests being of the order of 30 MHz.

By way of example, in the event that the amplitude of voltages Ua to Ucvaries from 0 to 24 V, and frequency F0 of the voltages is comprisedbetween 1 and 667 Hz, the amplitude of signals U1 and U2 isapproximately 2 V, and frequencies F1 and F2 are of the order of severalMHz.

Likewise, in order to avoid disturbing the supply of control voltages Uato Uc, i.e. in order to assure normal operation of motor 1, threefilters (not shown) can be connected respectively to output terminals 5a to 5 c of voltage generator 5, to filter the measurement linkedsignals (in particular signals U1 and U2), whose frequency is of theorder to several MHz, while not modifying voltages Ua to Uc. Preferably,said filters are made using three band stop filters each including acoil and a capacitor connected in parallel with the coil, these filtersblocking signals U1 and U2 whose respective frequencies F1 and F2 belongto the range of frequencies blocked by said band stop filters. By way ofvariant, said filters can be made using three low-pass filters includingthree respective coils series connected between outputs 5 a, 5 b and 5 crespectively, and connection terminals 2 a, 3 a and 4 a, respectivelyand three respective capacitors connected in parallel between respectiveoutput terminals 5 a, 5 b and 5 c and the device's earth.

As regards calculating means 26, it will be recalled that these meansare arranged to calculate the angular position from the two signals U1and U2.

FIG. 9 shows an embodiment of calculating means 26 of control device 20of FIG. 4. It will be noted in FIG. 9 that the elements of controldevice 20 which are identical to those described in relation to thepreceding Figures have been designated by the same references.

As FIG. 9 shows, calculating means 26 include a frequency-voltageconverter 71 and a processing circuit 72.

Frequency-voltage converter 71 includes an input terminal 71 a connectedto the output of operational amplifier 36 of FIG. 4, and an outputterminal 71 b connected to processing circuit 72. Converter 71 isarranged to receive signal U1 (respectively U2) via a terminal 71 a, andto convert this signal into a voltage X1 (respectively X2) which iscompatible with the operation of processing circuit 72, the amplitude ofthis voltage being proportional to the difference between frequency F1(respectively F2) and a known value of such frequency (for example,value Fmax or Fmin of FIG. 8). converter 71 is also arranged to supplyvoltage X1 (respectively X2) via a terminal 71 b. Preferably,frequency-voltage 71 is formed by a known frequency discriminator.

Processing circuit 72 includes an input terminal 72 a connected tooutput terminal 71 b of converter 71 and an output terminal 72 bconnected, in the example of FIG. 3, to voltage generator 5.Furthermore, processing circuit 72 is arranged to receive voltages X1and X2 via terminal 72 a, and to carry out operations enabling thesingle value of angular position θ corresponding to the couple {F1, F2}of frequencies F1, F2 represented by voltages X1 and X2 to bedetermined.

In order to better understand the operations carried out by processingcircuit 72, reference will again be made to FIG. 8. Thus, aninstantaneous measured voltage X1mes corresponds, by definition, to avalue of frequency F1 comprised between Fmax and Fmin, represented inFIG. 8 by the reference X1mes. As this Figure shows, voltage X1mescorresponds on curve 61 to two angular values θ2 and θ3 comprisedbetween 0 and 180°. Likewise, an instantaneous measured voltage X2mescorresponds on curve 62 to two angular values θ4 and θ5. It will benoted that two values among values θ2 to θ5 (in the present case θ3 andθ4) are congruent modulo 180°, which defines the existence of a singlevalue comprised between 0 and 180°. In other words, it corresponds tothe couple {X1mes, X2mes} a single value which is equal to value θ3associated with curve 61, or to value θ4 associated with curve 62, thissingle value being desired angular position θ.

In practice, given that curves 61 and 62 of FIG. 8 are identical to eachother, at an offset close to 120°, processing circuit 72 is programmedto contain a single correspondence table between voltage X1 or X2 andangular value θ, this table being similar to a conventionaltrigonometric table between values Arc sin(θ) and the correspondingangular values θ. Processing circuit 72 is programmed to carry out thefollowing successive operations. A first operation consists indetermining, from said table, a first couple of angular values θ6 and θ7corresponding to voltage X1 received by terminal 72 a, as well as asecond couple of angular values θ8 and θ9 corresponding to voltage X2.And a second operation consists in determining, from among values θ6 toθ9, the two values the difference between which is 120° and, amongstthese two values, that which corresponds to curve 61, this value beingconsidered the desired angular position θ.

It will be noted that the value of 120° introduced into said secondoperation corresponds to the offset of 120° of curves 61 and 62 of FIG.8, this offset having already been mentioned hereinbefore. Thus, in theevent that the angular values corresponding to voltages X1mes and X2mesare determined from said table (and not from curves 61 and 62 of FIG.8), the existence of this offset has to be mathematically introduced bycalculating the differences between values θ6 to θ9, two of them havinga distance of 120° between them.

It will also be noted that the use of the correspondence table canrequire an additional initial operation which consists in normalizingvoltages X1mes and X2mes, from peak values of voltages X1 and X2 whichdepend on the components of the device.

It goes without saying that the results of the operations carried out byprocessing circuit 72 do not provide exact values but approximatevalues. By way of improvement, a third measurement frequency F3 could beprovided, for example during a third configuration Y3, which allows theaccuracy of angular position θ obtained during these calculations to beincreased.

Preferably, processing circuit 72 is made using a conventional 32 bitmicroprocessor. This microprocessor is programmed to carry out theaforementioned programs in particular.

As shown in FIG. 4 in conjunction with FIG. 9, processing circuit 72 canalso be programmed to provide, via terminal 72 c, control signal U3 byswitching means 34, so as to define a measurement cycle divided intothree phases, so that, during the first and second phases, measuringmeans 24 respectively have configurations Y1 and Y2 to providecalculating means 26 with respective signals U1 and U2 and, during thethird phase, calculating means 26 determines the desired angularposition.

Purely by way of example, FIG. 10 shows a timing diagram 91 of signalU3. Reference t0 designates an initial instant from which the firstphase of a measurement cycle starts, reference t1 designates the instantwhen this first phases finishes and the second phase of the same cyclestarts, reference t2 designates the instant when this second phasefinishes and the third phase of the same cycle starts, and reference t3designates the instant when this third phase finishes and a newmeasurement cycle starts. Signal U3 has a value <<0>> during the firstphase, and <<1>> during the following phases. By way of illustration, itwill be noted that the time interval between instants t0 and t1, as wellas that between instants t1 and t2, is comprised between 50 and 100 μs,and that the time interval between instants t2 and t3 is comprisedbetween 400 and 600 μs.

It goes without saying for those skilled in the art that the abovedetailed description can undergo various modifications, alternativeembodiments and improvements without departing from the scope of thepresent invention.

By way of variant, the device according to the present invention can bearranged to control a motor including a greater number of stator coilsthan three. In such case, the connections between the motor and thepower supply means, as well as those between the motor and the measuringmeans, are arranged to be suited to the number of stator coils of themotor.

Also by way of variant, the measuring means of this device can include aswitching circuit which is not controlled by the processing circuit, butwhich is connected to independent control means.

Also by way of variant, the measuring means can be arranged to measurefrequencies F1 and F2 simultaneously, unlike the measuring means of FIG.4 in which these frequencies are measured sequentially during ameasurement cycle as described above. FIG. 11 shows a second embodimentof the control device according to the present invention, designated bythe reference 99, which includes detection means 100 provided withmeasuring means 101 as mentioned above, and calculating means 104. Itwill be noted in FIG. 11 that elements of control device 99 which areidentical to those described in relation to the preceding Figures, havebeen designated by the same references. Measuring means 101 include twoamplification circuits 102 and 103 identical to amplification circuit 35of FIG. 4. Measuring means 104 include two frequency-voltage converters105 and 106 identical to frequency-voltage converter 71 of FIG. 9, and aprocessing circuit 107 also similar to processing circuit 72 of FIG. 9.Essentially, it will be noted that amplification circuit 102 isconnected to form configuration Y1 of FIG. 5, and that amplificationcircuit 103 is connected to form configuration Y2 of FIG. 6, so thatsignals U1 and U2 are provided simultaneously by calculating means 104.

Those skilled in the art will note that, in the event that frequenciesF1 and F2 are simultaneously provided to the calculating means, eachoperational amplifier 36 of the two amplification circuits 102 and 103cannot be connected to motor 1 via capacitors 37, 38 and 40, like thedevice of FIG. 4. Indeed, if this was the case, measurement signals U1and U2 would be simultaneously present at the terminals of operationalamplifiers 36 of the two circuits 102 and 103, which would mean that thetwo frequencies F1 and F2 could not be differentiated. For this purpose,three coils 37 a, 38 a and 40 a are connected respectively in serieswith capacitors 37, 38 and 40, so as to form respectively three bandpass filters tuned to a predetermined frequency, so that the filters ofamplification circuit 102 are tuned to frequency F1 of signal U1provided by circuit 102, and the filters of amplification circuit 103are tuned to frequency F2 of signal U2 provided by circuit 103.

By way of improvement, the processing circuit can command, during a samemeasurement cycle, at least one additional configuration of theswitching circuit, in order to provide a third frequency to increase theaccuracy during detection of the rotor angular position, by saidprocessing circuit.

Also by way of improvement, the processing circuit can also beprogrammed to be able to calculate, from successively determined angularposition values, the number of revolutions made by the rotor, as well asthe speed and acceleration of the rotor, and monitor the evolution ofthese different parameters over time.

Let us consider the calculation of the number of revolutions made by therotor. Processing circuit 72, 107 can be programmed to store the angularposition (or first value) determined at the end of a first measurementcycle, and the angular position (or second value) determined at the endof the following measurement cycle (or second cycle), and to calculatethe difference between the second value and the first value, thisdifference providing the value of the movement made by the rotor duringthe second cycle, i.e. the desired number of revolutions.

Let us consider now the calculation of the rotational speed of therotor. The processing circuit can be programmed to calculate thedifference between two angular positions measured at the end of firstand second consecutive measurement cycles, as is described hereinbefore,and to calculate the ratio of this difference over the period of ameasurement cycle, this ratio providing the value of the speed of therotor during said second cycle.

Likewise, in order to calculate the rotor acceleration, the processingcircuit can be programmed to calculate the difference between two speedsof the rotor measured at the end of first and second consecutivemeasurement cycles, as is described above, and to calculate the ratio ofthis difference over a measurement cycle, this ration providing theacceleration value of the rotor during said second cycle.

Let us consider the monitoring of the different parameters. Theprocessing circuit can be programmed to compare angular position θ, thenumber of revolutions made, the speed or acceleration of the rotor at apredetermined comparison value.

By way of example, angular position θ can be compared to a theoreticalvalue θs representing the ideal synchronism situation. It will berecalled in this regard that a transmission between the stator and rotorof an electric motor is called <<synchronous>> when the rotational speedof the rotor is equal to that of the rotating field. It will also berecalled that, during such a transmission, an increase in the resistanttorque applied to the rotor causes an increase in the angular offsetbetween the magnetic position of the rotor and that of the rotatingfield and that, beyond a certain value θd, the rotor is pulled out ofsynchronism.

Also by way of example, the comparison value of angular position θ cancorrespond to an angular position offset with respect to synchronismvalue θs, this angular offset being able to cause a sufficient motortorque for the rotor to drive a predetermined load.

Also by way of example, angular position θ can also be compared to thepulling out of synchronism value θd, so as to check whether this offsetis less than pulling out of synchronism value θd, i.e. to check whetherthe motor has fallen out of synchronism.

What is claimed is:
 1. A device for controlling an electric motorprovided with a rotor fitted with a permanent magnet magneticallycoupled to at least first, second and third stator coils connected tofirst, second and third connection terminals, said device including:means for providing, via first, second and third output terminals,first, second and third respective control signals to said first, secondand third connection terminals of said motor, respectively, said signalsbeing periodic at a control frequency; and detecting means for detectingan angular position of the rotor; wherein said detecting means includes:measuring means arranged to be able to be connected to said first,second and third connection terminals, said measuring means forming withsaid first, second and third stator coils at least first and secondoscillating circuits having respectively first and second distinctelectric configurations, so that the first and second oscillatingcircuits can provide respectively first and second periodic measurementsignals having first and second frequencies, respectively, that aresubstantially higher than said control frequency and that varyperiodically with the angular position of said rotor, at a periodcorresponding to a complete rotation of the rotor divided by the numberof poles of said permanent magnet; and calculating means arranged toreceive the first and second measurement signals, calculate said angularposition from the couple formed by the first and second frequencies ofsaid signals and to provide a value of said angular position.
 2. Acontrol device according to claim 1, wherein said first and secondmeasurement signals have amplitudes substantially lower than those ofsaid control signals.
 3. A control device according to claim 1, furtherincluding at least first, second and third filtering means connectedbetween, on the one hand, said first, second and third output terminals,respectively, and on the other hand said first, second and thirdconnection terminals, respectively, so that the first and secondmeasurement signals do not disturb the normal operation of the motor. 4.A control device according to claim 3, wherein each of said filteringmeans includes a band-stop filter.
 5. A control device according toclaim 3, wherein each of said filtering means includes a low-passfilter.
 6. A control device according to claim 1, wherein said measuringmeans includes: a switching circuit arranged to receive a control signaland to form sequentially, in response to said signal, the connections ofthe measuring means to said connection terminals in accordance with saidfirst and second electric configurations; and an amplification circuitarranged to provide said first and second measurement signals at saidfirst and second respective frequencies, when said switching circuitforms said first and second electric configurations, respectively.
 7. Adevice for controlling an electric motor provided with a rotor fittedwith a permanent magnet magnetically coupled to at least first, secondand third stator coils connected to first, second and third connectionterminals, said device including: means for providing, via first, secondand third output terminals, first, second and third respective controlsignals to said first, second and third connection terminals of saidmotor, respectively, said signals being periodic at a control frequency;and detecting means for detecting an angular position of the rotor;wherein said detecting means includes: measuring means arranged to beable to be connected to said first, second and third connectionterminals, said measuring means forming with said first, second andthird stator coils at least first and second oscillating circuits havingrespectively first and second distinct electric configurations, so thatthe first and second oscillating circuits can provide respectively firstand second periodic measurement signals at first and second respectivefrequencies which are themselves periodic functions of the angularposition of said rotor, at a period corresponding to a complete rotationof the rotor divided by the number of poles of said permanent magnet;and calculating means arranged to receive the first and secondmeasurement signals, calculate said angular position from the coupleformed by the first and second frequencies of said signals and toprovide a value of said angular position, wherein said measuring meansincludes: a switching circuit arranged to receive a control signal andto form sequentially, in response to said signal, the connections of themeasuring means to said connection terminals in accordance with saidfirst and second electric configurations; and an amplification circuitarranged to provide said first and second measurement signals at saidfirst and second respective frequencies, when said switching circuitforms said first and second electric configurations, respectively; andwherein said amplification circuit includes an operational amplifierwhose output terminal is intended to be connected via a first capacitorto one of said first, second and third connection terminals and to thecalculating means, a non-inverting input of said amplifier beingintended to be connected via a second capacitor to one of the tworemaining connection terminals, and wherein an inverting terminal ofsaid operational amplifier is intended to be connected, via a thirdcapacitor, to the other of said remaining connection terminals.
 8. Acontrol device according to claim 7, wherein said switching circuitforms said first configuration so that the output terminal of saidoperational amplifier is connected to said first connected terminal viasaid first capacitor, wherein the non-inverting input terminal of saidamplifier is connected to said second connection terminal via saidsecond capacitor and wherein the inverting input terminal of saidamplifier is connected to said third connection terminal via said thirdcapacitor.
 9. A control device according to claim 7, wherein saidswitching circuit forms said second configuration so that the outputterminal of said operational amplifier is connected to said secondconnection terminal via said first capacitor, wherein the non-invertinginput terminal of said amplifier is connected to said first connectionterminal via said second capacitor, and wherein the inverting inputterminal of said amplifier is connected to said third connectionterminal via said third capacitor.
 10. A control device according toclaim 7, wherein said calculating means includes: a frequency-voltageconverter arranged to receive said first and second measurement signals,to convert these signals into first and second electric voltages whichrepresent respectively said first and second frequencies, and to providesaid voltages; and a processing circuit arranged to: receive said firstand second electric voltages; to carry out operations allowing a singlevalue corresponding to the couple formed by said first and secondfrequencies contained respectively in said first and second electricvoltages to be determined; and to supply said single value as being saidvalue of the angular position.
 11. A control device according to claim10, wherein said processing circuit is arranged to supply said controlsignal to said switching circuit, so as to define a measurement cycleduring a first phase of which said measuring means has said firstconfiguration and a second phase of which said measuring means has saidsecond configuration.
 12. A device for controlling an electric motorprovided with a rotor fitted with a permanent magnet magneticallycoupled to at least first, second and third stator coils connected tofirst, second and third connection terminals, said device including:means for providing, via first, second and third output terminals,first, second and third respective control signals to said first, secondand third connection terminals of said motor, respectively, said signalsbeing periodic at a control frequency; and detecting means for detectingan angular position of the rotor; wherein said detecting means includes:measuring means arranged to be able to be connected to said first,second and third connection terminals, said measuring means forming withsaid first, second and third stator coils at least first and secondoscillating circuits having respectively first and second distinctelectric configurations, so that the first and second oscillatingcircuits can provide respectively first and second periodic measurementsignals at first and second respective frequencies which are themselvesperiodic functions of the angular position of said rotor, at a periodcorresponding to a complete rotation of the rotor divided by the numberof poles of said permanent magnet; and calculating means arranged toreceive the first and second measurement signals, calculate said angularposition from the couple formed by the first and second frequencies ofsaid signals and to provide a value of said angular position; whereinsaid measuring means includes: a first amplification circuit includingan operational amplifier whose output terminal is connected, via a firstcapacitor and a first coil connected in parallel with said firstcapacitor, to said first connection terminal and to the calculatingmeans, a non-inverting input terminal of said amplifier being connected,via a second capacitor and a second coil connected in parallel with saidsecond capacitor, to said second connection terminal, and wherein aninverting terminal of said operational amplifier is connected, via athird capacitor and a third coil connected in parallel with said thirdcapacitor, to said third connection terminal; and a second amplificationcircuit including an operational amplifier whose output terminal isconnected, via a first capacitor and a first coil connected in parallelwith said first capacitor, to said second connection terminal and to thecalculating means, a non-inverting input terminal of said amplifierbeing connected, via a second capacitor and a second coil connected inparallel with said second capacitor, to said first connection terminal,and wherein an inverting terminal of said operational amplifier isconnected, via a third capacitor and a third coil connected in parallelwith said third capacitor, to said third connection terminal.
 13. Acontrol device according to claim 12, wherein said calculating meansincludes: a first frequency-voltage converter arranged to receive saidfirst measurement signal, to convert said signal into a first electricvoltage representative of said first frequency and to supply saidvoltage; a second frequency-voltage converter arranged to receive saidsecond measurement signal, to convert said signal into a second electricvoltage representative of said second frequency and to supply saidvoltage; and a processing circuit arranged to: receive from said firstand second frequency-voltage converters said first and second electricvoltages respectively; to carry out operations allowing a single valuecorresponding to the couple formed by said first and second frequenciescontained respectively in said first and second electric voltages to bedetermined; and to supply said single value as being said value of theangular position.
 14. A control device according to claim 12, whereinsaid processing circuit is programmed to contain a correspondence tablebetween a first plurality of frequency values and a second plurality ofangular position values, said first and second pluralities being linkedto each other in accordance with one of said periodic functions to saidperiod corresponding to a complete rotation of the rotor divided by thenumber of poles of said permanent magnet.
 15. A control device accordingto claim 14, wherein said operations of said processing circuitcomprise, during a measurement cycle: determining, from saidcorrespondence table, first and second angular position valuescorresponding to said first frequency contained in said first electricvoltage, and third and fourth angular position values corresponding tosaid second frequency contained in said second electric voltage;determining the single couple formed by one of said first and secondvalues and one of said third and fourth values, so that the differencebetween these two values is equal to an angular offset between twoconsecutive stator coils of said motor; and supplying that of said firstand second values of said single couple, as being said single value. 16.A control device according to claim 15, wherein said processing circuitis programmed to compare said angular position obtained at the end ofsaid operations to a predetermined comparison value, so as to monitorthe evolution of said rotor angular position over time.
 17. A controldevice according to claim 16, wherein said comparison value is equal toa value representing an ideal synchronism situation.
 18. A controldevice according to claim 16, wherein said comparison value is equal toa value able to cause a sufficient motor torque to drive a load appliedto the rotor.
 19. A control device according to claim 16, wherein saidcomparison value is a value representing the pulling out of synchronismof the motor.
 20. A control device according to claim 15, wherein saidprocessing circuit is programmed to: store as first position a referenceangular position or the angular position calculated at the end of afirst measurement cycle, and as second position the angular positioncalculated at the end of the following or second measurement cycle; tocalculate the difference between said second position and said firstposition, said difference representing the angular displacement value ofthe rotor during said second cycle, and to compare said angulardisplacement to a predetermined comparison value; so as to monitor theevolution of the number of revolutions made by said rotor over time. 21.A control device according to claim 15, wherein said processing circuitis programmed to: store as first position a reference angular positionor the angular position calculated at the end of a first measurementcycle, and as second position the angular position calculated at the endof the following or second measurement cycle; to calculate the ratio ofsaid difference between said second position and the first position overthe measurement cycle period, said ratio representing a value of therotational speed of the rotor during said second cycle, and to comparesaid rotational speed to a predetermined comparison value; so as tomonitor the evolution of the rotational speed of said rotor over time.22. A control device according to claim 21, wherein said processingcircuit is programmed to: store as first speed the rotational speed ofthe rotor calculated at the end of said second measurement cycle, and assecond speed the speed calculated at the end of the followingmeasurement cycle or third cycle; calculate the ratio of the differencebetween said second speed and said first speed over a measurement cycleperiod, said ratio representing an acceleration value of the rotorduring said third cycle; and compare said acceleration value to apredetermined comparison value, so as to monitor the evolution of saidrotor's acceleration over time.
 23. A control device according to claim10, wherein each frequency-voltage converter includes a frequencydiscriminator.
 24. A control device according to claim 10, wherein saidprocessing circuit includes a 32 bit microprocessor.
 25. A controldevice according to claim 13, wherein each frequency-voltage converterincludes a frequency discriminator.
 26. A control device according toclaim 13, wherein said processing circuit includes a 32 bitmicroprocessor.
 27. A control device according to claim 10, wherein saidprocessing circuit is programmed to contain a correspondence tablebetween a first plurality of frequency values and a second plurality ofangular position values, said first and second pluralities being linkedto each other in accordance with one of said periodic functions to saidperiod corresponding to a complete rotation of the rotor divided by thenumber of poles of said permanent magnet.
 28. A control device accordingto claim 27, wherein said operations of said processing circuit consist,during a measurement cycle: determining, from said correspondence table,first and second angular position values corresponding to said firstfrequency contained in said first electric voltage, and third and fourthangular position values corresponding to said second frequency containedin said second electric voltage; determining the single couple formed byone of said first and second values and one of said third and fourthvalues, so that the difference between these two values is equal to anangular offset between two consecutive stator coils of said motor; andsupplying that of said first and second values of said single couple, asbeing said single value.